The invention relates to a process for preparing magnesium nitrate hexahydrate by reacting magnesium oxide or magnesium carbonate with nitric acid in the presence of water. The invention also relates to a process for preparing thermally stable ammonium nitrate containing granules using the magnesium nitrate hexahydrate obtained by converting magnesium oxide or magnesium carbonate with nitric acid in the presence of water.
A process for preparing magnesium nitrate hexahydrate starting from magnesium oxide, nitric acid and water is known from U.S. Pat. No. 1,844,862. According to this known process, finely divided magnesium oxide is added to dilute nitric acid while stirring, the amount added being sufficient for complete conversion, after which the mixture is allowed to settle, the solid matter is filtered off, the remaining solution is evaporated and finally magnesium nitrate hexahydrate is crystallized out by cooling. As the magnesium oxide is added, the mixture is cooled to maintain a temperature of 71.degree. C. until almost all of the magnesium oxide is added. Subsequently the temperature is raised at the end of the reaction period to facilitate neutralization of the reaction mixture.
A disadvantage of this known process is that a large proportion of the impurities introduced with the magnesium oxide go into solution. Subsequently after cooling the impurities crystallize out to a large extent along with the magnesium nitrate hexahydrate thereby yielding an impure product. This impure product is not easily filtered. The filtering difficulties necessitate the use of filtering aids.
Another disadvantage of this process is that in its practical realization, that is in commercial production processes, the excess of water which is always introduced must subsequently be removed through evaporation.
Using this product in preparing thermally stable ammonium nitrate granules causes additional problems such as severe fouling of the evaporators in the ammonium nitrate plant. If a prilling technique is employed, this impure prior art product clogs the spray openings of the prilling bucket.
The present invention provides a process in which the above-mentioned disadvantages do not or hardly occur. It is therefore the object of the present invention to provide a method for the preparation of a magnesium nitrate hexahydrate by converting magnesium oxide or magnesium carbonate with nitric acid in the presence of water whereby the resultant product is purer than that obtained from the known processes, does not contain excess water, does not foul evaporators in ammonium nitrate plants, and does not clog prilling process equipment.